In succulent plants the stomata open in night and close in day. Which among the following would be best hypothesis to explain the mechanism of stomatal action in night only.

• CO₂ accumulates, reduces pH, stimulate enzymes resulting in accumulation of sugars.

• Increase in CO₂ concentration, conversion of organic acids into starch resulting in the increased conversion into sugars resulting in K⁺ transport.

• Low CO₂ concentration accumulates organic acids resulting in the increased concentration of cell sap.

• CO₂ used up, increase pH results in accumulation of sugars.

B.

Increase in CO₂ concentration, conversion of organic acids into starch resulting in the increased conversion into sugars resulting in K⁺ transport.

In CAM plants stomata open at night. In these plants night acidification occurs. i.e., malic acid is
synthesised during night due to incomplete oxidation of carbohydrates.
In night. 2 C ₆H₁₂O₆₊ 3 O₂$\to$ 3 C ₄H₆O₅+ 3H₂O
                                             (malic acid)
                                                    $↧$
                                leads to opening of stomata

At night malic acid formed in guard cells dissociates into H and malate ions. K ion exchange from subsidiary cells with H ions. Thus due to accumulation of K ions osmotic pressure of guard cells increases, endosmosis occurs and guard cells become turgid due to which stomata opens. The malic acid at clay time breaks into CO₂ and pyruvic acid thus increasing the concentration of CO₂ in mesophyll cells. This is utilised in Calvin cycle to form sugar which is finally converted into starch.